1. Field of the Invention
This invention relates to a balloon catheter used primarily in medical treatment and surgery for the purpose of dilating lesion sites such as strictures or blockages in passages in the body, and more particularly to a balloon catheter used in percutaneous translumin angioplasty (PTA) and percutaneous translumin coronary angioplasty (PTCA), etc., for forming peripheral blood vessels, coronary arteries, and valves.
2. Description of the Related Art
Balloon catheters are used primarily in internal passage anaplasty performed on internal passages that have become constricted or blocked. In general, a balloon catheter is structured such that it has a balloon connected to an expansion lumen for supplying a pressurized fluid in the leading end portion of a tubular catheter shaft having a plurality of lumens in the interior thereof, and such that it has ports that connect to the lumens in the base end part. In its normal condition the balloon is folded up against the catheter shaft. An example of PTCA therapy is now described wherein this type of balloon catheter is used. First, a guide catheter is inserted from the site of centesis, and passed through the aorta, and the leading end thereof is positioned at the entrance to a coronary artery. Next, the guide wire inserted into and passed through the guide wire lumen is advanced until it passes the stricture in the coronary artery, whereupon the balloon is inserted along the guide wire and made to be colocated with the stricture. Then, using a hypodermic syringe or the like, a pressurized fluid is passed through the inflation lumen to the balloon, the balloon is inflated, and that stricture is subjected to dilatation therapy. After the stricture has been sufficiently dilated, the balloon is made to contract under reduced pressure, folded up, and removed to the outside of the body, whereupon the PTCA is finished. In the procedure here exemplified, the description is of an example of use in coronary stenosis dilatation, but the balloon catheter is widely used in dilatation therapy in other vascular lumen and in the somatic cavity.
Balloon catheters are mainly inserted into internal passages that are being treated, and dilatation therapy conducted by introducing internal pressure at the site of therapy. Accordingly, what are demanded therein in terms of functional characteristics are sufficient strength so that the balloon does not fail when pressure necessary for inflation is introduced, and the capability of being controlled safely at desired inflation sizes. In many cases, moreover, particularly in the vascular system, it is necessary to effect insertion from the insertion opening along a blood vessel to the lesion or prescribed site to achieve the object of therapy, and for that reason the controllability of the catheter is crucial.
The catheter is generally configured of a long, slender, tubular member. It must be manipulated so that it is passed from the insertion opening on the outside of the body through sites inside the body that are curved or that have become narrow and constricted. For that reason, forces applied to the end of the catheter on the outside of the body must be effectively communicated to the leading end part, and flexibility is also required to be able to cope with curved parts. In addition, because the catheter is usually used with a guide wire passing through the interior thereof, another important characteristic is that the friction resistance of the catheter against the guide wire be small so that it can always be moved smoothly, so that there is no loss in the communication of forces applied. In order to realize these controllability factors, several particulars are demanded in terms of the configuration of a balloon catheter in general, namely (1) that the leading end (distal) portion exhibit flexibility so that it can follow curved internal passages well, (2) that the operator-end (proximal) portion exhibit some degree of strength so that forces are communicated well to the distal end, and (3) that the tubular member or members exhibit low friction and good sliding properties in order to keep friction resistance low in order to pass the guide wire. In order to satisfy these demands, catheters are usually made of a polyethylene, or a high-strength polyamide, or a high-strength polyamide elastomer.
What is a particularly critical flexibility property is the flexibility of the balloon portion, and vicinity thereof, at the distal end of the catheter. That part is of course soft, and will often be inserted into curved segments, and, furthermore, it slides against the softest portion of the guide wire that is inserted in the interior thereof. It is therefore required that there be no discontinuity in this flexibility. The reason is that, when the catheter is deployed in a curved segment, if there is discontinuity in the flexibility, discontinuity will also develop in the way the catheter bends, the guide wire resistance in that portion will become significantly larger, and that will cause controllability to decline.
At the distal end of a catheter, in general, a fixed portion of the tubular member exists as a foremost end “tip,” the purpose whereof is to pass the balloon and guide wire. When this tip portion is hard, the difference in flexibility with the guide wire emerging from the tip becomes great, the guide wire readily bends at that place, and, as a result, a large decline in controllability ensues.
In the case of a lesion site at which calcification has advanced, moreover, when an attempt is made, after the guide wire has been passed through such a site, to pass the balloon catheter through along the guide wire, if the tip portion is hard, a phenomenon is observed very frequently where the tip portion hangs up at the lesion site that has calcified and hardened, so that it cannot be passed through.
In recent years, furthermore, in vascular dilatation therapy, frequent use is made of a metal dilatation piece that remains in place, generally called a stent. It is necessary to pass the balloon catheter through the inside of the stent, both in order to perform anaplastic dilatation after stent dilatation (post-dilatation), and when strictures have reformed inside the stent or on the distal side of the stent. If at such time the tip portion is hard, similarly as the calcified lesion, a problem arises in that the balloon catheter catches on the metal stent and will not pass.
As described earlier, it is important to make the leading end portion of the balloon catheter—and especially the tip portion-flexible, and so as not to exhibit a large difference in hardness with the other portions of the catheter. In terms of methods for fabricating the tip portion, there is the method of securing the balloon and the tubular member for passing the guide wire with an adhesive, and the method of securing them by fusion. Whereas there is a tendency for the tip portion to become harder due to the presence of a layer of the adhesive used with the adhesive method, with the fusion method, not only is there no layer of adhesive, but making the diameter thinner by a thermal process is easier during fusion or after fusion, wherefore the fusion method is advantageous for effecting flexibility.
However, in conventional catheters, polyethylene, which is a polyolefin material, and particularly high-density polyethylene exhibiting high low-friction properties, has been frequently used in the tubular member for passing the guide wire (i.e. the guide wire passing tubular member). As a low-friction material, high-density polyethylene is outstanding, but it is poor in terms of fusability and bondability with the other main materials, and cannot be fused with any other than a polyolefin material, wherefore only bonding means have been available with other materials. With balloons made of polyolefin materials, it is impossible of make the skin thin in the portion that becomes fusion material due to the need for cross-linking in the material, wherefore, as a result, it has not been possible to make the tip portion flexible even by fusion. High-density polyethylenes that exhibit outstanding low friction properties are inferior in flexibility, while the low-density polyethylenes that are comparatively flexible are almost never used because the friction and sliding properties decline precipitously as the flexibility thereof increases. And when a polyethylene single-layer tubular member is used for the guide wire passing tubular member, it has been very difficult to impart adequate flexibility to the tip portion.
There are also commercially available balloon catheters that are configured with a two-layer tube, with the inside of the tubular member for passing the guide wire made of polyethylene and the outside made of polyamide, using a polyamide for the balloon having the same properties as that tubular member. However, it has not been possible thereby to impart sufficient flexibility to the tip portion because polyamides generally have a higher elastic modulus than polyethylenes.
There are also commercially available balloon catheters that are configured with a polyamide elastomer balloon and a guide wire passing tubular member made of a polyamide elastomer having higher hardness and a higher melting point than the balloon, wherein the balloon and the tubular member are fused together, but the tip portions thereof have not been adequately flexible because a harder material is deployed in the guide wire passing tubular member than in the balloon.
That being so, the object that a first invention would achieve is to provide a balloon catheter exhibiting outstanding controllability, and outstanding flexibility in the tip portion that is an improved distal-side foremost end in the catheter.
Furthermore, various properties other than those described in the foregoing are required in the balloons. Taking a PTCA balloon catheter as an example, when dilating a hard stricture that has calcified or where a stent has been left in place, high pressure-withstanding strength becomes necessary, but materials exhibiting high pressure-withstanding strength tend generally to lack flexibility. In order to reach that stricture through a narrow, curved vascular lumen, however, high flexibility and thin balloon skin are required. This balloon flexibility is closely related to the performance of the balloon when causing it to cross (pass) or recross (repass) a stricture (i.e. the crossing or recrossing performance). If balloon flexibility is not maintained, recrossing performance declines, particularly when reusing the balloon.
Another characteristic that is required is that vascular walls not be impaired by over-dilation when the balloon is subjected to high pressures during the dilatation of hard strictures. That is, the limitation on the elongation in the radial dimension relative to the inflation pressure in the balloon (compliance characteristic) is very critical. The compliance characteristic is classified into and defined at three different levels, based on differences in responsiveness to inflation pressure, namely: (1) non-compliant, the level of compliance characteristic wherewith elongation is most limited, defined as a rate of change in balloon diameter of 2% to 7% when the inflation pressure ranges from 6 atm to 12 atm, (2) semi-compliant, defined as a rate of change in balloon diameter of 7% to 16% relative to the same variation in inflation pressure, and (3) compliant, defined as a rate of change in balloon diameter of 16% to 40% relative to the same variation in inflation pressure.
In order to prevent over-dilatation of vascular walls when dilating hard strictures under high pressure, the balloon compliance characteristic should be semi-compliant, and preferably non-compliant. However, although the ideal balloon exhibits abundant flexibility, high pressure-withstanding strength, and suitable elongation (compliance characteristic), these characteristics are mutually contradictory from the perspective of the physical properties of the balloon material. With a view to realizing good balance in these mutually contradictory characteristics, many advanced technologies are being developed wherein the polymer blend materials represented below are used.
One example of an advanced technology wherein a polymer blend material is applied in a limited way to a balloon is seen in the “balloon for use in medical treatment apparatuses, consisting of a thermoplastic elastomer” described in TOKUHYO H9-506008 (published). Disclosed in this publication are a balloon wherein is used a blend material of an engineering thermoplastic elastomer and a polymer material for use in non-flexible structures, and a layered balloon comprising a non-flexible structural polymer layer and a flexible and wear-resistant thermoplastic elastomer layer.
In TOKUHYO H10-506562 (published) (“expansion balloon containing a polyester ether amide copolymer”), an expansion balloon is disclosed which comprises a single polymer layer containing a polyester ether amide copolymer and also a polyamide such as nylon, wherein, when that polymer layer contains a polyether amide, that polyether amide comprises ester bonds.
And in Japanese Patent Application Laid-Open No. H8-127677 (published (“polymer blend for use in medical treatment apparatus comprising a catheter and a balloon for an expansion catheter”) is disclosed a polymer blend material for medical use that comprises a first polymer component selected from a group made up of polyesters and polyamides, and a second polymer component that exhibits a Shore hardness of less than D75, selected from a group made up of polyolefins, ethylene copolymers, polyester block copolymers, and polyamide block copolymers.
In all of these advanced technologies described above, use is made of a blend material containing a flexible elastomer and a non-elastomer for eliciting high strength. However, in these advanced technologies, balloon flexibility and strength vary greatly according to the ratio in which the two components are mixed, and there has been a problem in that optimizing the mixture ratio is very difficult. In the case of the layered balloon described in TOKUHYO H9-506008 (published), moreover, the extrusion molding process for fabricating the tubular parisons that are the raw materials for the balloons is demandingly complex, is problematic in terms of higher production costs, and also involves the possibility that inter-layer peeling will occur in the layered balloons that are fabricated.
Thereupon, in view of the problems described above, an object of a second invention is to provide a balloon catheter wherein is used a balloon made from a polymer blend material that features a good balance of adequate pressure-withstanding strength, adequate flexibility, and suitable compliance characteristics.
Furthermore, lesion site dilatation therapy is not limited to a one-time treatment, but usually requires a number of dilatation treatments. The reason therefore is that, when the balloon is removed from the body after dilatation therapy, and it is then confirmed by imaging that the stricture has not been completely dilated, the procedure must be repeated until the stricture is completely dilated, and the balloon guided to that lesion site and inflated.
When such a balloon catheter product is provided, the balloon is in a condition wherein it is collapsed, and folded around the guide wire passing tubular member with the outer diameter thereof minimized. Accordingly, when it is used the first time, the balloon will pass the stricture without difficulty. Then the balloon is inflated by raising the internal pressure therein. However, when removing the balloon to the outside of the body, even if it is collapsed under reduced pressure, it will not return to the original folded condition, and a phenomenon (called winging) occurs wherein the balloon, squashed flat, spreads out horizontally in the diameter dimension so that two wings are formed. The overall length of those two wings becomes larger not only than the outer diameter of the balloon in the folded condition, but also larger than the nominal diameter of the balloon. Thus there is a problem in that it is very difficult to perform repeat dilatation treatments using the same balloon. More specifically, there are times when the tapered parts of the balloon that has been divided in two by the two wings strikes the stricture in the lumen of the blood vessel and refuses to advance any further. This is believed to be due to the tapered part on the distal side forming a severe step when winging occurs. When such a winged balloon is passed to a lesion site that is hardened due to calcification or stent emplacement, the technician feels a very large resistance. If that balloon is then advanced forcibly, there is a considerable danger that the stent will be pushed to the distal side of the blood vessel, moving the stent out of position.
The same kind of problems as described above are described in detail in Japanese Patent No. 2671961 (published), wherein is disclosed a balloon catheter wherewith the balloon can be restored to a folded condition without inducing winging. This balloon catheter comprises a balloon that has (a) vertical groove(s) in the longitudinal direction. When the balloon is inflated, the vertical groove(s) disappear(s), and when collapsed the balloon is returned to a condition wherein it is folded along the vertical groove(s).
With the balloon described in the publication cited above, however, the vertical groove(s) remain(s) when the balloon is inflated unless the internal pressure applied is at least as high as a certain level, and there is a problem in that the outer cross-sectional shape will not become truly circular. If the outer cross-sectional shape will not become truly circular, a stricture cannot be dilated evenly about its entire circumference, and the danger of the stricture reforming within a short time is high.
In view of the problems described in the foregoing, an object that a third invention would achieve is to provide a balloon catheter wherewith the high resistance forces encountered when pushing the balloon in due to the effects of winging are sharply reduced when repassing the balloon catheter through a hard lesion site where calcification has occurred or a stent is in place.
The leading end of a balloon catheter is usually protected prior to use by being already covered with a protective device, and when the balloon catheter is to be used in a procedure that protective device is pulled off. One of the reasons for using this protective device is to protect the balloon portion from damage prior to use. When bending or other damage has been inflicted on the balloon portion, the balloon can easily scratch the vascular inner walls when it is passed through a vascular lumen. Also, the guide wire lumen gets bent also, and the resistance force encountered when pushing the balloon catheter in increases. Thus it becomes very difficult to guide the balloon accurately to the lesion site. Also, when a balloon that has sustained damage is inflated, there is a great danger of the balloon bursting or the pressurized fluid leaking, and there are cases where this has led to a serious medical accident.
The second reason for using a protective device is to make the outer diameter of the balloon as small as possible right up until immediately before a procedure is performed. This is because, the smaller the balloon outer diameter relative to the vascular lumen, the smaller the contact area between the vascular wall and the balloon, and the smaller the resistance force encountered when pushing the balloon in. Thus minimizing the balloon outer diameter makes it easy to guide the balloon to the lesion site. And in lesion sites that are very difficult or have a high curvature, and in sites where the surface resistance is high, such as inside stents, the lesion site passability of the balloon is enhanced by keeping the balloon outer diameter small.
There are cases where, before performing a procedure, and after removing the protective device from the balloon catheter, the guide wire lumen is flushed or filled with physiological saline solution to prevent thrombogenesis, and also of soaking the outer surface of the balloon catheter in physical saline solution. With the type of balloon catheter wherein the guide wire lumen communicates from the base end of the catheter to the leading end thereof (commonly called “over-the-wire type”), particularly when flushing, it is only necessary to supply the physiological saline solution or other flushing fluid through a port in a manifold provided at the base end of the catheter, and flushing is easy. With a monorail type balloon catheter, however, the situation is unlike that with an over-the-wire type. In a monorail balloon catheter, a distal-side shaft and a proximal-side shaft are joined, the balloon is joined to the distal end of the distal-side shaft, there is a manifold equipped with a port for supplying the pressurized fluid to the balloon at the base end of the proximal-side shaft, and a guide wire lumen is formed inside the distal-side shaft along the long axial dimension thereof. The back end opening of the guide wire lumen is provided midway along the shaft, wherefore flushing fluid cannot be supplied to the guide wire lumen from the manifold provided on the base end side of the catheter. That being so, conventionally, a hypodermic needle having an outer diameter roughly the same as or slightly smaller than the internal diameter of the leading end opening of the guide wire lumen is inserted into that leading end opening, a hypodermic needle holding member for holding that hypodermic needle is fit to the hypodermic barrel, flushing fluid is supplied to the guide wire lumen, and flushing is performed.
However, the outer diameter of the balloon catheter leading end is extremely small, running from approximately 0.5 mm to 3.0 mm or so. Therefore, when a hypodermic needle is inserted into the guide wire lumen from the leading end opening, not only is that operation very intricate, but trouble readily ensues, such as the leading end becoming bent or deformed into a trumpet shape, or otherwise damaged. When that happens, it becomes extremely difficult to guide the balloon all the way to the lesion site during the procedure.
In view of the problems described in the foregoing, an object of a fourth invention is to provide a balloon catheter that is provided with a protective device wherewith it is possible to flush the balloon catheter guide wire lumen without involving an intricate operation, and without damaging or deforming the leading end of the balloon catheter.